The present invention relates to an apparatus for removing dust and offensive odor generated from ascon, and, more particularly, to an apparatus for removing dust and offensive odor generated from ascon, wherein air pollutants, harmful dust and offensive odor generated during the production of ascon are removed or minimized by a batch system, thus preventing environmental pollution.
Generally, ascon (asphalt-concrete) is produced by mixing an aggregate, such as gravel, crushed stone or the like, and an additive with concrete obtained by the fractional distillation of crude oil and heating the mixture under a predetermined condition, and is generally used as a road pavement material or the like.
A process of producing ascon proceeds as follows. First, an aggregate transferred from a cold bin to a conveyor belt passes through a dryer to remove moisture from the aggregate, the moisture-removed aggregate is heated to a temperature at which the aggregate can be suitably mixed with asphalt oil (AP oil), the heated aggregate passes through a hot elevator, a hot screen and a hot bin to adjust the particle size thereof, and then the particle size-adjusted aggregate is introduced into a mixer and then mixed with a suitable amount of heated asphalt oil (AP oil) supplied from an asphalt oil storage tank through a measuring tank, thereby producing ascon.
The produced ascon is immediately loaded on a truck, and then is applied to a road pavement site. The process of producing ascon needs five major units including a ‘storage unit’ for storing an aggregate and stone powder, a ‘drying unit’ (dryer) for drying an aggregate and the like, a ‘mixing unit’ for mixing a heated aggregate with asphalt, a ‘dust collecting unit’ for preventing air pollution, and a ‘shipping unit’ for shipping ascon. Among the five major units, four, excluding the storage unit, are closely related with the discharge of offensive odor and pollutants.
Methods of discharging air pollutants from the process of producing ascon are largely classified into two types: ducted emission and fugitive emission.
Ducted emission is referred to as a method of discharging air pollutants after purifying them using pollutant treatment equipment. In this case, air pollutants are chiefly discharged from a hot elevator, a hot screen, a hot bin or a mixer.
In contrast, fugitive emission is referred to as a method of discharging fly dust generated during the procedure of shipping ascon or the procedure of storing and conveying an aggregate.
That is, one of the major air pollutants is an organic fume generated by the volatilization of dust and asphalt (AP) oil. The organic fume, which is an offensive odor-causing material, is discharged from the process of mixing an aggregate dried by a dryer with AP oil supplied from an AP oil storage tank in a hot mixer and the process of loading a truck with the produced ascon.
The major air pollutants includes ammonia-based compounds, aldehydes, aromatics, which are obtained by evaporation of asphalt (AP) oil at high temperature, in addition to the organic fume (volatile organic compounds (VOCs), which is obtained by the mixing of high-temperature aggregate and asphalt (AP) oil). Specific examples thereof are given in Table 1 below.
TABLE 1Ammonia-basedAldehydesClass.compoundsisobutyl valericAromaticsComponentsammonia trimethylaminealdehydealdehyde toluene xylene styreneMinimum0.150.000110.00090.000710.920.110.033detectableconcentrationType of odor urinerotten fishmoldunpleasantrubbersweetrubberMeasured2.20.0030.910.0346.910.00.41concentration
Further, the conditions and methods of deodorizing air pollutants are given in Table 2 below.
TABLE 2Ammonia-basedAldehydesClass.compoundsisobutylvalericAromaticsComponentsammoniatrimethylaminealdehyde aldehydetoluenexylenestyreneMinimum0.150.000110.00090.000710.920.110.033detectableconcentrationMeasured2.20.0030.910.0346.910.00.41concentrationConcentration152810124889113index ofoffensive odorCombustion◯◯◯◯◯◯◯methodAbsorption◯◯XXXXXmethodAdsorption◯◯◯◯◯◯◯methodBiological◯◯◯◯ΔΔΔmethodNeutralization◯◯XXXXXmethod◯: treatableΔ: treatable (suitable contact time)X: non-treatableConcentration index = measured concentration/minimum detectable concentration
Further, the minimum detectable concentrations of air pollutants emitting offensive odor are given in Table 3 below.
TABLE 3Minimum detectable concentrations of air pollutants emitting offensive odor(unit: ppm)MinimumdetectableNo.Componentsconcentration1Ammonia0.152Methyl mercaptan0.000123Hydrogen sulfide0.00054Methyl sulfide0.000125Methyl disulfide0.000286Trimethylamine0.000117Acetaldehyde0.00158Propionaldehyde0.00159N-butylaldehyde0.0003210Iso-butylaldehyde0.000911N-valeric aldehyde0.0007112Iso-valeric0.00019aldehyde13Iso-butanol0.01214Ethyl acetate0.2515Methyl isobutyl0.17ketone16Toluene0.9217Styrene0.03318Xylene0.1119Propionic acid0.002420N-butyl acid0.00006821N-valeric acid0.000122Iso-valeric acid0.000053
As described above, offensive odor and pollutants generated during the process of producing ascon are principal causes of severe environmental pollution, and are problematic as follows.
First, they cannot be easily observed by the naked eye.
Second, since they are discharged sporadically rather than continuously from open-air facilities and field operations, and are also discharged from only a single source, their generation sources are various, and investment efforts for their removal are less effective compared to removal of other air pollutants.
Third, since their characteristics are complicated in many aspects due to the discharge of various kinds of materials to the air, the results of environmental pollution caused thereby are attributable to various kinds of compounds rather than to a single material.
Fourth, it is very difficult to objectively measure, via an analyzer, human perception of various offensive odors and pollutants detected in a unit of ppm, and the detection of offensive odors may change depending on time, place, concentration and composition.
However, the deodorization methods given in Table 2 above are not perfect because they have their respective advantages and disadvantages. Therefore, the most effective deodorization method must be selected in consideration of the kind and concentration of offensive odor-causing materials, process change, installation area, work line, temperature, humidity, airflow, secondary pollution management measures, fuel usage and the like. However, there are many difficulties in excessive installation cost, management cost, maintenance cost and the like.
In order to solve the above-mentioned problems, an apparatus has been proposed for removing dust and offensive odor using a dryer in an ascon plant (Korean Patent Application No. 10-2007-37310, filed on Apr. 17, 2007, and then registered). The technical gist thereof is described as follows.
An apparatus for removing dust and offensive odor using a dryer in an ascon plant, in which the ascon plant includes a dryer for heating an aggregate discharged from a cold bin, a hot elevator for conveying the aggregate heated by the dryer, an additive supply unit, a dust supply unit, and a mixer for mixing the heated aggregate conveyed by the hot elevator with an additive supplied from the dust supply unit and dust supplied from the dust supply unit to produce ascon and discharging the produced ascon through an outlet, the apparatus comprising: an intake fan for forcibly sucking offensive odor emitted from the inside of the mixer and discharging the offensive odor to the dryer; a back filter disposed between the mixer and the intake fan and serving to collect dust in the mixer and then transfer the collected dust to the hot elevator; a hood for forcibly sucking the offensive odor generated at the time of discharging the ascon through the outlet of the mixer and then discharging the offensive odor to the dryer.
The dryer of the apparatus is provided with an intake fan for sucking air for fuel combustion, and the intake fan forcibly sucks air mixed with offensive odors through the hood.
The above-mentioned registered technology can remove parts of harmful gases and the like generated from ascon, but, as described above, is problematic in that it cannot be completely applied under various environments or circumstances.